Past Events

Abstract: Thousands of exoplanets -- planets beyond our own solar system, orbiting stars other than our sun -- have been discovered over the last twenty years; indeed, we now know that our galaxy contains more planets than stars. The study of exoplanets has now moved on from the discovery phase to the characterisation of all these planets, with the ultimate goal of understanding whether some of them are habitable, and whether any actually harbour life. In this talk, I will discuss how we find and study exoplanets, what we have learned so far about their properties and habitability, and prospects for identifying the signatures of alien life in the not-too-distant future.

Abstract: In this talk I will show how the dynamics on vertically stable terrestrial oceans are influenced by mesoscale eddies, while those on an icy moon's ocean are likely to be governed by convection.

In the first part of the talk, I will focus on terrestrial eastern boundary currents. One would expect that a narrow boundary current on the eastern boundary would broaden and eventually dissipate towards the west due to the influence of Rossby waves. The role of topography in trapping such currents at the boundary is well-known. I show that eddies could perform such trapping even in the absence of topography. Additionally, the boundary layers, predominantly the eastern downwelling one, are broadened by the westward drift of aforementioned eddies. This has implications for the location of deep water formation sites.

In the second part of the talk, I will focus on global oceanic circulation on icy moons. The overarching goal of this study is to decipher the likely ocean circulation in terms of quantities that could be relatively easily observed from space (rotation rate, bottom heating, and depth of the ocean). I perform numerical simulations to characterize the nature of convection in terms of non-dimensional numbers. The learnings from the non-dimensional numbers could then be applied to other icy moons not covered by simulations. Moreover, I find that oceans in which small convective plumes are not resolved tend to transfer most of the bottom heat to the ice shell near the equator thereby indicating thinner equatorial ice sheet. On the other hand, oceans with plumes tend to transfer heat to the ice sheet near the poles indicating thinner polar ice sheet.

Abstract: Unprecedented sea ice loss and an amplified warming have been observed over the Arctic in the recent decade and is expected to continue in future climate projections. At the same time, an increasing frequency of extreme winter events across North America and Europe has gained socio-economic attention. Possible linkage between the Arctic warming and Northern Hemisphere midlatitude circulation has been suggested but remains inconclusive. In this talk, I will focus on the remote influence of the Arctic warming and the underlying dynamical mechanism. Specifically, I’ll discuss how the troposphere-stratosphere dynamical coupling mechanism can play an important role in this teleconnection using a hierarchy of models and observations.

Observations of about 5000 extra-solar planets (exoplanets) have revealed a much larger chemical and physical diversity than found in the Solar System. The recently-launched James Webb Space Telescope is expected to characterize the atmosphere of large terrestrial exoplanets. The atmosphere of terrestrial exoplanets is formed as a result of outgassing and influenced by the chemistry (mineralogy) of the interior. How different can an exoplanetary interior (e.g., carbon-rich) be from that of Earth? Which extreme mineralogies can exist? What is the role of surface mineralogy in regulating the atmospheric composition of (e.g., carbonate-silicate cycle)? What can observations tell us about chemical conditions on terrestrial exoplanets? I will attempt to answer some of these questions with the help of experimental and theoretical tools from geosciences.

Space Physics, or Heliophysics, is the study of the medium between the Sun and the planets in our solar system, and the medium between stars and their planets. The space between stars and their planets is filled with a continuous flow of plasma, also called ''Solar/Stellar wind, and this outflow can impact the top of the atmosphere of planets on a short- and long range. Moreover, the interaction can be affected if the planet has an internal magnetic field. In my talk, I will review the modeling approach of solar and stellar wind. I will also discuss how the solar/stellar wind interacts with the planetary/exoplanetary atmosphere.

Continents, plate tectonics and life make our Earth unique in the solar system and perhaps, in the entire universe (at least, so far). However, none of them was present when  the planet formed some 4.56 billion years ago (Ga). Therefore, understanding how, when, and why they appeared is critical to understand planetary evolution and habitability. My work directly deals with these questions. For the past few years, I am working on elucidating in what form plate tectonics appeared on the early Earth (> 2 Ga) and what imprints it left on the different system components of the planet (e.g., crust-mantle, hydrosphere, atmosphere etc.). I find answers to these questions by integrating the classical approaches ofsolid Earth geology (field geology and petrology) with the novel methods like diffusion modelling of micron-scale compositional zonings in minerals to unravel geological timescales  (diffusion chronometry) and numerical modelling of large-scale tectonics (100s-1000s of km). So far, my studies have revealed that plate tectonics processes were substantially different > 2 Ga  from their modern nature and, for the first time, showed how timescales of large-scale processes can help us identify it from the natural rock record. In particular, I proposed a new style of continent-continent collision (called peel-back orogenesis) for that time period, which is found to have massive implications for building continents and driving the rise of O₂ in the atmosphere.

Interstellar Polycyclic Aromatic Hydrocarbon (PAH) molecules exist in diverse forms depending on the local physical environment of the Interstellar Medium (ISM). Formation of ionized PAHs is favorable in the extreme condition of the ISM. Besides its pure form, PAHs are likely to exist in substituted forms, for example, PAHs with functional groups, nitrogenated PAHs, protonated and deuterated PAHs, etc. These PAHs may convert into alternate forms as a result of ongoing chemical processes in the ISM. The spectral evidence of PAH molecules and its variants in the ISM are observed via the mid-infrared emission bands, particularly at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 μm. These bands, also known as ‘Aromatic Infrared Bands (AIBs)’ are widely observed towards a varied range of astronomical sources and arise from the vibrational relaxation of PAH molecules on absorption of background UV photons. However, the exact form of PAH molecules that are responsible for the AIBs is still ambiguous. Here, we discuss a few of the possible forms of interstellar PAH molecules (for example: deuteronated, nitrogenated and aliphatic PAHs etc.) as carriers for AIBs. Density Functional Theory (DFT) calculation on several classes of PAHs is employed to study its spectral characteristics in infrared which is compared with the observed bands in quest of any similarity that establishes its presence in the ISM.

Abstract: The interaction of UV radiation with molecules (photochemistry) plays a key role in the surface-atmosphere system of rocky planets. In this talk, I will explore how photochemistry controls the chemical context in which life arose on Earth, and affects the molecular signposts with which we hope to detect life elsewhere. I will specifically discuss (1) photochemical insights into sulfur and nitrogen speciation in natural waters on early Earth, (2) the UV environment on planets orbiting Sunlike stars compared to M-dwarf exoplanets, and (3) the accumulation of potential biosignature gases in rocky planet atmospheres. I will connect each of these theoretical studies to empirical advances, such as the discovery of new pathways for prebiotic ribonucleotide synthesis, a possible opportunity to use exoplanets to test theories of the origin of life, and the recent discovery of phosphine on Venus. I will conclude by emphasizing the synergistic roles of experiment and theory.